Rules Governing UK Landing Cards

Dear Sir or Madam,

I am trying to find information on the laws and processes relating
to landing cards for visitors arriving into the UK.

It is my understanding that, under the 1971 Immigration Act, these
forms are "in such form as the Secretary of State may direct".

However I cannot find any further detail as to what the current
requirements are.

I would expect that as well as any Statutory Instrument(s) or
equivalents, there will have also been explanation forms for
visitors, policy documents and training manuals for immigration
officials, etc. I am also interested in what changes to all of
these have been made since 1971.

At this point I am primarily seeking assistance in relation to
discovering what information exists, rather than requesting copies
of such documents now. However where information is already
publicly available I would also appreciate you pointing me to it.

For clarity, I am interested in all information relating to UK
landing forms: what data is required, in what format, etc. and how
the requirements and/or the forms have changed since 1971.

Thank you in advance for your assistance.

Yours faithfully,

Richard